Wet spinning of cellulose triester



United States Patent Delaware N0 Drawing. Filed Nov. 3, 1959, Ser. No. 850,531 14 Claims. (Cl. 1854) The present invention relates to the wet spinning of organic acid esters of cellulose containing fewer than about 0.29 free hydroxyl group per anhydroglucose unit of the cellulose molecule, particularly cellulose triacetate.

US. patent application Serial No. 730,021, filed April 21, 1958, in the name of Jesse L. Riley, now Patent No. 3,057,039, discloses the wet spinning of a solution of a cellulose triester into a coagulant or spin bath which contains both a non-solvent and a solvent for the cellulose triester, the spin bath exerting a swelling action on the freshly formed filaments. Preferably the cellulose triester is cellulose triacetate having an acetyl value of at least about 60% and generally above 61% calculated as combined acetic acid and is employed as a solution of about 18 to 26% concentration by weight in a solvent comprising a halogenated lower alkane which may contain up to about 15% by weight of a lower alkanol, e.g. methylene chloride plus methanol. The spin bath is preferably also made up of the halogenated al-kane and alkanol, except that the alkauol proportion is sufficiently high to ef fect precipitation of the cellulose triacetate. The halogenated alkane concentration may range from about 25 to 65% by weight of the spin bath, its concentration desirably varying inversely with the temperature of the spin bath which may range from about room temperature up to about the boil, e.g. about 15 to 45 C. When the halogenated alkane concentration in the spin bath C is approximately related to the spin bath temperature T by the equation C=75%Ti5 it has been found that the resulting filaments, under the prevailing spinning conditions, will simultaneously exhibit higher tenacity and elongation than if the spin bath concentration is varied slightly either up or down.

The resulting products exhibit excellent physical properties and can readily be distinguished from other filamentary materials such as dry spun cellulose triacetate, for example.

The individual filaments are generally substantially circular in cross-section, in contrast to the bulbous or potato-shaped cross-section of dry-spun filaments. Also, stress-strain curves for the wet-spun cellulose triacetate filaments show a higher modulus of elasticity and higher resistance to deformation throughout the whole range of strain, as compared with dry-spun cellulose triacetate filaments.

The filaments produced in accordance with the Riley .u'isclosure exhibit tenacities in excess of about 1.8 and usually 2 grams per denier at elongations of at least about 18 and usually 20%, even for filaments whose denier is in the range of 1.5 to 4. The energy of rupture, i.e. the area under the stress-strain curve from zero stretch to break, is high, above 800 dyne cm. for 1 cm. of a 3 denier filament. These filamentary materials are characterized by radial uniformity. This can be determined by treating the filamentary materials with a saponifying agent which deesterifies the surface portions of the filamentary material, forming a cellulose skin which is then removed with a solvent for cellulose. When subjected to this treatment a filamentary material which is non-uniform exhibits different properties as compared with the original material, while a radially uniform material has the same properties as before.

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In testing (for radial uniformity the surface removal can be effected, for example, by wetting the filaments to be tested in cold water containing 0.1 gram per liter of Triton X-100 (iso-octyl phenyll ether or polyethylene glycol) then immersing them in 1000 times their weight of a 50 grams per liter solution of sodium hydroxide at C. for from 30 seconds to 3 minutes, and quickly transferring them to cold running water for 5 minutes. The filaments are then soured in acetic acid for 15 minutes, and again rinsed in running water for 15 minutes. After drying in air, the filaments are immersed at room temperature for 3 minutes in a solution made up of equal weights of cupriethylene diamineand water to dissolve the cellulose skin formed by the saponification. The filaments are then rinsed, soured, rinsed and dried as before.

The foregoing treatments of course reduce the filament denier but the tenacity in grams per denier is not changed. The percent elongation also remains unchanged. X-ray diffraction patterns, microscopic observations and other properties are also the same for the starting material and for specimens from which surface layers of different thickness are removed. The safe-ironing temperature following heat treatment is also the same whether or not the filament is de-surfaced.

Whereas surface removal of dry spun cellulose triacetate effects a marked increase in the rate of dyeing, surface removal of wet-spun cellulose triacetate filamentary material does not similarly affect the dyeing rate. This is demonstrated as follows: Dry spun cellulose triacetate filaments of 3.75 denier when immersed in a dyebath took up 0.18% of their weight of dyestulf after being immersed in the dyebath for 5 minutes and 0.22% of their weight after =15 minutes immersion. If these filaments are first treated as described to remove a surface layer 44x10 cm. thick, the filaments under identical dyeing conditions will pick up 0.22% by weight of dyestuif in 5 minutes and 0.30% in 15 minutes. This appreciable increase in pick up evidences radial heterogenity in the filaments.

By way of comparison, 2.5 denier wet-spun filaments pick up 0.24% by weight of dyestutf after being immersed 5 minutes in the dyebath previously set forth and 0.34% after 15 minutes. Removal of a surface layer 47x10 cm. thick does not increase the dyeing rate. Actually there is a slight decrease to 0.23% and 0.31% in 5 and 15 minutes, respectively, i.e. approximately the same rate as dc-surfaced dry spun cellulose triacetate filaments. This slight decrease in the dyestuif pick up rate of desurfaced wet spun filaments as opposed to wet spun fila ments which have not been tie-surfaced is due to the fact that the wet spun filaments initially have a slightly pebbled surface which is smoothed out upon de-surfacing thereby reducing slightly the surface to volume ratio of the filaments.

In the above tests the dyebath was water containing 50 grams per liter of dispersed Amacel Red 2B (a red cellulose acetate dye), 1 gram per liter of Igepon T-5 l (a dispersing agent) and 1 gram per liter of sodium hexametaphosphate; the bath was maintained at 95 C.

The Riley filamentary materials show a relatively high overall birefringence after complete saponification of said materials. The overall birefringence of the saponified material is above about 0.031, typical values being in the range of about 0.034 to 0.037. This overall birefringence is the sum of the birefringence through the fiber and is measured, in conventional manner, by a transmission technique. In the complete saponification method employed for this purpose, the filamentary material is saponified completely by immersion for atleast 30 minutes in times its weight of a solution containing, by weight,

5 parts of sodium hydroxide, 12 parts of sodium acetate, parts of dimethyls-ulfoxide and 73 parts of water, at 80 C. Completion of saponification can be checked by wetting the filamentary material with l-N cupriethylene diamine solution; if, as viewed under a microscope, the filamentary material dissolves completely in 30 seconds, saponification is complete; if not complete, the time of immersion in the saponifying liquor can be increased. When it has been determined that saponification is complete, the filamentary material is rinsed with distilled water until the rinse water is neutral. The saponified material is air dried. The treatment does not cause shrinkage or loss of strength. The overall birefringence, as opposed to merely surface birefringence, is determined in customary manner, as with a Berek compensator using olarized light.

Cellulose triacetate filamentary materials produced in accordance with the Riley disclosure exhibit definite rubbery properties at elevated temperatures. This is demonstrated in the following manner: A 125 denier 40 filament yarn is held at constant length (e.g. 10 inches) and heated to a temperature of 220 C. at a just perceptible initial tension (about 0.03 g.). The temperature is then cycled between 217 C. and 223 C. It will be found that the tension on the filament increases as the temperature increases and decreases very perceptibly as the temperature decreases, typical of a rubber. By way of comparison, if the temperature'of the filament is cycled between 162 C. and 168 C., the. tnesion will be found to decrease as the temperature increases, typical of a glass.

Like other cellulose triacetate filamentary material, the Riley cellulose triacetate filamentary material may be heat treated to raise the safe ironing temperature of fabrics produced therefrom and to improve the dimensional stability, resistance to creasing, permanence of pleating, and the like. However, the wet-spun filamentary mate rial shows substantially no shrinkage or decrease of tenacity on such heat treatment. In fact, the tenacity may even increase. For example, a filament having an original tenacity of 2.15 grams per denier, when heat treated in air at 210 C. for 5 minutes shrinks less than 1% and has a final tenacity of 2.37 g./den.

Cellulose triacetate filamentary material produced in accordance with the Riley invention is also characterized by resistance to creep at elevated temperature. This is demonstrated as follows: One end of a filament is anchored within a horizontal heating tube. 10 inches from the anchored end, the filament is knotted to a glass filament which extends outside the tube and runs over a pulley. A weight is suspended from the protruding end of the glass filament. With various size weights suspended from the glass filament the tube is heated and the displacement of the weight with change in temperature is noted. Cellulose triacetate filaments produced by dry spinning the initial solutions begin to creep at about 168 C. The wet-spun filamentary materials do not creep comparably below about 178183 C. The rate and amount of creep for dryspunrfilaments under a load of 0.033 gram per denier are only reached for the wet-spun filamentary material at a load equal to or in excess of 0.067 gram per denier.

In producing such filaments they occasionally exhibit a tendency to coalesce or adhere to one another. One way to overcome this tendency and to avoid coalescence is described in US. patent application Serial No. 729,980; filed April 21, 1958, in the name of John W. Soehngen, now Patent No. 3,057,038, and involves the removal of the adherent spin bathfrom-the freshly formed swollen w filaments while the filaments are maintained separated and substantially tensionless, as by passage through an air jet provided with hot air. This treatment also serves to introduce a crimp into the filaments with no physical damage such as accompanies mechanical crimping. The crimps in adjacent filaments of the bundle or tow are randomly arranged, out of alignment; the crimp being threedimensional, either helically or randomly threedimensional, and not substantially in a single plane. Thus, the tow is much more voluminous or lofty than the conventional tows. When the tow is cut into staple fiber lengths and then processed in the conventional manner to produce staple fiber yarn, much less break-age of filaments and formation of undesirable short filaments or fly takes place. Also, because of the voluminous character of the material, much less mechanical processing is necessary to open or separate the staple fibers before they are formed into yarns.

Typical crirnped filaments contain 8 or more, e.g. 8 to 12, fine crimps per inch, the amplitude of the crimp being irregular but generally being onthe order of 1 mm. and the percent crimp, based on the straightened length, being above about 4%. Percent crimp is defined as Straightened lengthcrimped length Straightenecl length While this procedure overcomes the tendency to coalesce, it has been :found that if the resulting tow is in tended to be formed into a staple fiber yarn by the steps of completing drying, lubricating, cutting into staple fibers, carding to produce a sliver and spinning it is sometimes necessary to repeat the carding step to produce a sliver which will yield a satisfactory yarn upon spinnmg.

It is an object of the present invention to provide an alternate procedure for avoiding coalescence of the wet spun filaments of cellulose triesters.

It is a further object of the invention to provide a process which permits production of cellulose triester filamentary material of improved physical properties.

Another object is to provide a process for producing cellulose triester filamentary material which can easily be handled in staple fiber form and can be converted into yarn in conventional manner.

Other objects and advantages of the invention will be apparent from the following detailed description and claims, wherein all proportions are by weight unless otherwise specified.

In accordance with one aspect of the present invention the cellulose triester dope is extruded into a spin bath exerting a swelling action thereon in the presence of a member selected from the group consisting of hydrocarbon oils, silicone oils, and poly-lower alkylene glycols. Representative materials include poly-dimethyl-siloxane, polyethylene glycol and the copolymer of ethylene and propylene oxides having molecular weights ranging from about 600 to 6000. From the standpoints of cost, tensile properties and physical condition of the product the best results are obtained using a hydrocarbon oil which is incorporated in the spin bath. Desirably, the hydrocarbon oil is a white mineral oil having an essentially aliphatic base, such as parafiinic or naphthenic base, and having a viscosity of about 30 to 400 seconds as measured at 38 C. (100 F.) in the Saybolt Universal viscosimeter, and preferably a viscosity of about 40 to 100 seconds. Its molecular weight desirably ranges from abouf to 400 and preferably about 200 to 300. Its initial boiling point generally is in excess of about 200 C. and preferably in excess of about 250 C. and its vapor pressure is generally less than about 0.1 mm. Hg at 38 C.

Based on the weight of the spin bath the hydrocarbon oil is generally present in about 0.1 to 3% and preferably about 0.5 to 1% to exert its beneficial effect to a substantial degree. Lower proportions result in a lesser improvement while higher proportions are less economical and do not appreciably improve the results achieved. If the mineral oil is added as a dispersion or solution along with other materials, e.g. pigments, anti-static agents or the like, the dispersion or solution is obviously added in amount sufficient to provide the desired percentage of the hydrocarbon oil component.

The exact proportion of hydrocarbon oil in the spin bath will vary with factors such as the feed ratio of spin bath to filamentary material, the denier and residence time of the filamentary material in the spin bath, the degree of extraction of spent spin bath from the filaments as they leave the spin bath, and the like. All factors considered, the concentration of hydrocarbon oil should generally be sufficient to leave about 0.1 to 5% and preferably about 0.5 to 2% of hydrocarbon oil on the filaments based on the dry weight of the filaments.

Upon leaving the spin bath the filaments can be dried in any desired manner and an anti-static agent may be applied if desired and if not previously applied either in the dope, the spin bath or to the wet filaments.

The hydrocarbon oil surprisingly improves the spinning stability, i.e. at a given spinning speed there are fewer broken fils or for a given number of fil breaks the maximum permissible spinning speed is higher with hydrocarbon oil in the spin bath. While not wishing to be bound thereby it is believed that the hydrocarbon oil retards the rate of coagulation of the filaments. At any rate, the filaments exhibit higher tenacities and/ or elongation than when no hydrocarbon oil is in the spin bath, the tensile factor, i.e. tenacity /elongation often being or more greater than without the hydrocarbon oil. The loop tensile properties are also improved by the pres ence of the hydrocarbon oil, the product exhibiting increased resistance to abrasion and fiexural fatigue.

The hydrocarbon oil is distributed substantially uniformly on the surface of the filaments, as contrasted with the discontinuous film produced by spraying or brushing hydrocarbon oil onto dry filaments. 'I he filaments exhibit little or no coalescence even in the absence of spe cial drying or aftertreatmen-ts. If cut into staple fiber, the staple fibers can be processed on conventional equipment with no special techniques. The spinning stability, physical properties, freedom from coalescence and physical properties for filaments extruded into spin baths containing mineral oil are superior to those for filaments which have been treated with mineral oil subsequent to leaving the spin bath.

While the invention has been described principally with reference to triesters of cellulose with acetic acid, it can be applied also to esters with formic, propionic, butyric, nitric, and like acids, as Well as to esters with mixtures of these acids with one another and/ or acetic acid.

The following examples are given to illustrate the invention further.

Example I A 22% solution in 9% methylene chloride/methanol of cellulose triacetate, having an acetyl value of 61.5% calculated as combined acetic acid, is extruded horizontally through an orifice having a diameter of 0.1 mm. into a 1 meter long bath of 41.5/58.5 methylene chloride/methanol at 35 C. and containing 0.5% by weight of the total bath of a white mineral oil having a viscosity at 100 F. of 50 Saybolt Universal seconds. The monofi-lament is taken up at a speed of 72 meters per minute and is 3 denier. Its tenacity is 2.09 grams ,per denier and its elongation is 26.2%, each of these values being several percent higher than the corresponding values for a monofilament produced identically except for the absence of mineral oil from the spin bath. The loop tenacity is increased by about 25% and the loop elongation by about 50% when mineral oil is in the spin bath, the loop tensile properties being obtained by bending two fibers into U-shape, hooking one through the other and pulling at each pair of free ends.

Example II The same dope as in Example I is extruded horizontally through a spinnerette having 40 orifices 0.1 mm. in diameter into a 42/58 methylene chloride/methanol spin bath at 35 C. and containing 0.12% by weight of the white mineral oil of Example I. 3 inches from the spinnerette the freshly formed filaments enter the flared en- 6 trance of a horizontal glass tube 26 inches long and 10 mm. in internal diameter through which the spin bath flows, concurrently with the coagulating filament bundle, at a linear velocity of 26 meters per minute. From the exit end of the spinning tube the yarn bundle is passed about three guides which separate it from the spin bath. The yarn then passes three times through a 2 inch internal diameter copper tube 53 inches long, between feed rolls operating at a peripheral speed of 150 meters per minute and then to a downtwister take up bobbin. Air at C. is blown through the copper tube to effect drying. The yarn is free of coalescence, has a soft hand and excellent physical properties; in the absence of mineral oil in the spin bath the filaments are coalesced to an appreciable degree and the yarn has a harsh or boardy hand.

Example III The process of Example II is repeated except'that the 0.12% of mineral oil is replaced by 1% by weight of the spin bath of polyethylene glycol (polyethylene oxide) having a molecular weight of about 1500. The product is free of coalescence.

Example IV The dope of Example -I is extruded upwardly through a spinnerette having 1396 holes 0.1 mm. in diameter into 41.7/58.3 methylene chloride/methanol at 34.7 C. and containing 2.3% based on total spin bath weight of the oil of Example I. From the spinnerette the freshly formed filaments travel 49 inches through a spinning column having an internal diameter of 1 inch. Fresh spin bath is supplied below the spinnerette at the rate of gallons per hour, moves in the same direction as the filaments and overflows at the top of the column. Spent spin bath is wiped away, the filaments pass between driven rolls operating at a peripheral speed of v80 meters per minute, they are separated from one another by passage through an air jet as described in application Serial No. 729,980 and are dried in tensionless condition. The driven roll speed of 80 meters per minute is several times the speed at which dope passes through the spinnerette, causing stretching or drawdown of the filaments to impart the desired physical properties. The filaments average 3 denier, contain 3.5% of the mineral oil, have a tenacity of 2.57 grams per denier, an elongation of 24.5%, and a tensile factor of 12.7.

Example V The process of Example IV is repeated except that the spin bath contains 0.5% of a composition containing 45.8% of the mineral oil of Example IV, 20% triethanolamine ester of coconut oil acids, 28.5% phosphate of C alkanols averaging C 3.2% triethanolamine, and 2.5% di-tertiaryamyl-phenol. The filaments contain 0.9% of the above materials, their tenacity averages 2.49 grams per denier, their elongation 25.3% and their tensile factor 12.5. Control filaments produced without the indicated composition in the bath have a tensile factor of 11.5. When the novel filaments are cut into staple fiber they can easily be processed into spun yarns by conventional equipment. 1

It is to be understood that the foregoing detailed description is given merely by [way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention wvhat we desire to secure by Letters Patent is:

1. The process which comprises extruding a solution of a cellulose triester into a coagulant spin bath in the presence of a minor amount of a member selected from the group consisting of hydrocarbon oils, silicone oils and poly-lower alky-lene glycols.

2. The process according to claim 1 wherein said member is present in the spin bath in an amount ranging from about 0.1 to 3% by weight.

3. The process which comprises extruding a solution of a cellulose triester into a coagulant spin bath to form filaments in the presence of a suflicient amount of a member selected from the group consisting of hydrocarbon oils, silicone oils and poly-lower alkylene iglycols, to deposit on said filaments about 0.1 to of said member based on their weight.

4. The process which comprises Wet spinning a solution of a cellulose triester into a spin bath including a minor amount of a hydrocarbon oil.

5. The process which comprises wet spinning a solution of a cellulose triester into a spin bath including a minor amount of a silicone oil.

6. The process which comprises wet spinning a solution of a cellulose triester into a spin bath including a minor amount of a poly-lower alkylene glycol having a molecular Weight ranging from about 600 to 6000.

7. The process which comprises wet spinning a solution of a cellulose triester into a spin bath exerting a swelling action on said cellulose triester and containing about 0.1 to 3% by weight of an aliphatic hydrocarbon oil.

8. The process which comprises wet spinning a solution of an organic acid ester of cellulose having fewer than about 0.29 free hydroxyl group per anhydroglucose unit of the cellulose molecule in a halogenated hydrocarbon solvent into a spin bath comprising about 25 to 65% of a halogenated hydrocarbon, a lower alkanol and about 0.1 to 3% by weight of a hydrocarbon oil.

9. The process according to claim 8, wherein said ester is cellulose acetate.

-10. The process according to claim 8, wherein said halogenated hydrocarbon is methylene chloride.

- digit 11. The process according to claim 8, wherein said lower alkanol comprises methanol.

12. The process according to claim 8, wherein said hydrocarbon oil is a mineral oil.

13. The process which comprises wet spinning a solution of cellulose acetate having an acetyl value of at least about by weight calculated as combined acetic acid in a solvent comprising methylene chloride and up to about 15% by weight of methanol into a spin bath comprising methylene chloride and methanol, the concentration of methylene chloride equalling approximately %:5-the temperature of the spin bath in C., said spin bath including about 0.1 to 3% by weight of white mineral oil having a viscosity at F. of about 30 to 400 Saybolt Universal seconds.

14. In the process for producing cellulose triester filaments having a tenacity in excess of about 1.8 grams per denier and an elongation in excess of about 18% by wet spinning a solution of the cellulose tri'ester itno a spin bath exerting a swelling action thereon and stretching the resulting filaments, the improvement which comprises incorporating in said spin bath a hydrocarbon oil.

References Cited in the file of this patent UNITED STATES PATENTS 1,997,632 Dreyfus Apr. 16, 1935 2,075,027 Dreyfius Mar. 30, 1937 2,424,743 Davis July 29, 1947 2,587,505 Moody Feb. 26, 1952 2,746,839 Terry et a1 May 22, 1956 2,764,468 Hare Sept. 25, 1956 

1. THE PROCESS WHICH COMPRISES EXTRUDING A SOLUTION OF A CELLULOSE TRIESTER INTO A COAGULAENT SPIN BATH IN THE PRESENCE OF A MINOR AMOUNT OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF HYDROCARBON OILS, SILICON OILS AND POLY-LOWER ALKYLENE GLYCOLS. 